The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board (PCB) attached to a disk drive base of the HDA. The head disk assembly includes at least one disk (such as a magnetic disk, magneto-optical disk, or optical disk), which is clamped to a rotating hub of a spindle motor. A head stack assembly (HSA) is actuated to position heads adjacent the major surfaces of the disk(s), to read and write information stored thereon. The printed circuit board assembly includes electronics and firmware for controlling the rotation of the spindle motor, for controlling the actuation and position of the HSA, and for providing a data transfer channel between the disk drive and its host.
The head stack assembly typically includes an actuator, at least one head gimbal assembly (HGA), and a flex cable assembly. Each HGA includes a head for reading and writing data from and to an adjacent disk surface. In magnetic recording applications, the head typically includes an air bearing slider and a magnetic transducer that comprises a writer and a read element. The magnetic transducer's writer may be of a longitudinal or perpendicular design, and the read element of the magnetic transducer may be inductive or magnetoresistive. In optical and magneto-optical recording applications, the head may include a mirror and an objective lens for focusing laser light on an adjacent disk surface.
The spindle motor typically includes the rotating hub (on which annular disks are mounted and clamped), a magnet attached to the hub, and a stator. Various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet, thereby rotating the hub. Rotation of the spindle motor hub results in rotation of the mounted disks. A disk clamp is typically attached to the rotating hub by threaded fasteners. The disk clamp typically includes a circular or annular contact surface that contacts and applies a clamping force to the top disk, so that it will rotate with the hub.
Many contemporary disk clamps are stamped from sheet metal to reduce their fabrication cost relative to disk clamps that are machined from a thicker metal stock. However, although stamped sheet metal clamps are desirably less expensive, the circular or annular contact surface may not be as flat. Poor flatness can cause unacceptably larger variation in clamping pressure around and near the disk inner diameter, which may in turn produce an undesirably larger warping of the clamped disk(s). Some of the resulting undesired curvature of the disk surface is known as “disk crown”.
Disk crown due to non-uniform clamping can undesirably modulate and affect the microscopic spacing between the disk surface and the adjacent read/write head. Such microscopic spacing affects the performance of the head in reading and writing, and so excessive disk crown can adversely affect the performance and signal to noise ratio (SNR) associated with disk drive operations.
Hence, manufacturers of contemporary disk clamps have striven to enhance the flatness of the circular or annular contact surface of the disk clamp, to help the disk clamp exert a more uniform clamping pressure on the top disk. One way manufacturers have done this is to subject the circular or annular contact surface of the disk clamp to lapping. Lapping is a form of grinding and/or polishing that can enhance the flatness of a surface by abrasive removal of material.
However, with contemporary stamped sheet metal disk clamp designs, lapping the circular or annular surface of the disk clamp causes such surface to significantly grow in area. That is, with contemporary stamped sheet metal clamp designs, lapping can cause the maximum effective clamping radius to increase and/or the minimum effective clamping radius to decrease. The amount of such increase or decrease may vary, depending on the rate of material removal during lapping, the duration of lapping, the clamp design, and local variations in the clamp geometry. Therefore, with contemporary stamped sheet metal clamp designs, lapping the circular or annular surface of the disk clamp may increase part-to-part variability in the effective clamping radius. Part-to-part variability in effective clamping radius is undesirable in a disk drive because it may cause undesirable part-to-part variation in disk dynamic behavior and/or read head to disk spacing.
Therefore, there is a need in the art for a disk drive having a stamped sheet metal disk clamp design that can reduce part-to-part variation that may result from lapping.